In ordinary installations of electric resistance heaters for space heating, such as for home, office or industrial buildings, the installation generally is engineered for the worst case or the most extreme weather conditions expected in the area. The consequence, of course, is that the installed heating power is larger than is necessary for a moderate day and is even larger than is necessary for a normal Winter day. Thus, the heating system normally is turned on and off frequently, and heating tends to be significantly uneven. This has numerous disadvantages, both in discomfort through the frequent on-and-off cycles and also as a consequence of the inefficiency resulting from constant heating and cooling. Face it: excessive capacity in an energy using device ends up wasting energy.
The problems of efficiency have recently become of increasing importance as a result of an energy shortage in much of the industrial world. Accordingly, it is highly desirable to make such improvements as will result in reduction of the consumption of energy. This need for energy conservation is so extreme that it is frequently necessary to accept and put up with significant discomfort and inconvenience. It is, therefore, both desirable and surprising to find that there can be an improvement in the efficiency of an operation coupled with an improvement in the comfort and convenience of the heating system.
Variable heating can be achieved by the use of two separate heating systems, one of lower capacity used for moderate heating requirements and another, of higher capacity, being used for more extreme requirements. One such system is disclosed in Boehm, U.S. Pat. No. 2,789,197. Such systems are expensive to install and usually result in the lower capacity system receiving excessive use and the higher capacity system receiving very moderat use. Similarly, controls that generate proportional power in a single system are expensive and, while desirable, have not been economically feasible.